Chromosome condensation is an essential cellular process that ensures the faithful segregation of genetic information during mitosis and meiosis. The long-term goal of this project is to understand how this dynamic and highly orchestrated process of DNA-protein assembly is achieved, and how it is regulated precisely during the eukaryotic cell cycle. A major emphasis will be made on the structural and functional characterization of 13S condensin, a recently identified protein complex that plays a key role in this process. 13S condensin is a DNA-stimulated ATPase that consists of two SMC (structural maintenance of chromosomes) subunits and three non-SMC subunits. The complex has an ability to reconfigure DNA by introducing global positive writhe in an ATP-dependent manner. In this proposal, (1) the five-subunit complex will be dissected biochemically to determine how individual subunits and subcomplexes contribute to condensin functions. (2) A cell cycle-dependent interaction between 13S condensin and chromatin will be reconstituted in vitro and the molecular basis of mitosis-specific condensation will be determined. (3) Structural, cell biological and biophysical approaches will be combined to understand when, where and how the condensin complex works in the context of higher-order chromosome structure. (4) New structural components that cooperate with 13S condensin to build up mitotic chromosomes will be identified and characterized. The information obtained from this work will ultimately contribute to a better understanding of human health because chromosome anomalies, such as aneuploidy and translocations, are tightly associated with tumor development or birth defects.